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xsk: fix potential lost completion message in SKB path 

The code in xskq_produce_addr erroneously checked if there
was up to LAZY_UPDATE_THRESHOLD amount of space in the completion
queue. It only needs to check if there is one slot left in the
queue. This bug could under some circumstances lead to a WARN_ON_ONCE
being triggered and the completion message to user space being lost.

Fixes: 35fcde7f8d ("xsk: support for Tx")
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Reported-by: Pavel Odintsov <pavel@fastnetmon.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Magnus Karlsson 2018-06-29 09:48:17 +02:00 committed by Alexei Starovoitov
parent d0fbad0aec
commit 20b52a7516
1 changed files with 2 additions and 7 deletions
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9
net/xdp/xsk_queue.h
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@ -62,14 +62,9 @@ static inline u32 xskq_nb_avail(struct xsk_queue *q, u32 dcnt)
return (entries > dcnt) ? dcnt : entries; return (entries > dcnt) ? dcnt : entries;
} }
static inline u32 xskq_nb_free_lazy(struct xsk_queue *q, u32 producer)
{
return q->nentries - (producer - q->cons_tail);
}
static inline u32 xskq_nb_free(struct xsk_queue *q, u32 producer, u32 dcnt) static inline u32 xskq_nb_free(struct xsk_queue *q, u32 producer, u32 dcnt)
{ {
u32 free_entries = xskq_nb_free_lazy(q, producer); u32 free_entries = q->nentries - (producer - q->cons_tail);
if (free_entries >= dcnt) if (free_entries >= dcnt)
return free_entries; return free_entries;
@ -129,7 +124,7 @@ static inline int xskq_produce_addr(struct xsk_queue *q, u64 addr)
{ {
struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring; struct xdp_umem_ring *ring = (struct xdp_umem_ring *)q->ring;
if (xskq_nb_free(q, q->prod_tail, LAZY_UPDATE_THRESHOLD) == 0) if (xskq_nb_free(q, q->prod_tail, 1) == 0)
return -ENOSPC; return -ENOSPC;
ring->desc[q->prod_tail++ & q->ring_mask] = addr; ring->desc[q->prod_tail++ & q->ring_mask] = addr;